1. Field of the Invention
The present invention relates to a thermal air flow sensor (air flow meter) for measuring the air flow (the amount of flowing) with use of a heating resistor. For example, the invention is concerned with an air flow sensor suitable for measuring the flow of intake air in an internal combustion engine.
2. Description of Related Art
As an air flow sensor installed in an intake passage of an internal combustion engine of an automobile or the like, a thermal type has come to be mainly adopted because it can detect a mass flow directly.
For example, such a thermal type air flow sensor uses, as air flow measuring elements, a heating resistor which makes heat exchange with intake air directly or indirectly and a resistor which compensates a change in air temperature at the time of measuring the air flow (sometimes also called a temperature compensating resistor, a thermal sensitive resistor, or a temperature measuring resistor), and controls an electric current flowing in the heating resistor so that a temperature difference between the heating resistor and the temperature compensating resistor becomes constant. This current value is converted into an electric signal to measure the air flow.
The heating resistor and the temperature compensating resistor have temperature dependence and for fabricating them there recently has been proposed a method of forming a thin film-like resistance area for air flow measurement on a semiconductor substrate such as silicon (Si) for example by using a micromachining technique for semiconductor. This method can mass-produce thermal air flow sensors relatively easily and is economical, so is now attracting attention as an air flow sensor capable of being driven with low electric power.
A semiconductor type air flow measuring device is disclosed, for example, in Japanese Patent Laid Open (Tokuhyo) No. 9-503310. According to the conventional technique disclosed in this publication, in a mass measuring apparatus for measuring an intake mass of an internal combustion engine, a sensor element is formed by etching a silicon wafer for example to form a diaphragm-like sensor region and forming plural resistance layers (one is a measuring resistor having temperature dependence and another is a heating resistor for heating the measuring resistor). As to a medium temperature resistance for compensating the temperature of a fluid medium, it is disposed on an outer surface of a casing of the mass measuring apparatus in order to avoid a thermal influence of the heating resistor.
According to another conventional technique, as disclosed, for example, in Japanese Patent Laid Open No. 2000-28411, a flow sensing section formed with a heating element and a temperature sensing element for flow measurement which is heated by the heating element, as well as a temperature sensing section formed with a temperature sensing element which makes air temperature compensation for flow measurement, are formed at one end of a substrate such as a silicon, alumina or glass substrate, and part of the substrate and output terminals are covered with a cover member by molding. In this conventional technique it is proposed to form a slit between the flow sensing section and the temperature sensing section for preventing the temperature sensing section from being thermally influenced by the flow sensing section.
In the thermal air flow sensor, as referred to above, a heating resistor and a temperature compensating resistor are used as air flow measuring elements.
In connection with an internal combustion engine, the supply of fuel is controlled in accordance with the value of air flow, but attempts have been made to utilize the intake air temperature in various automobile controls with use of an intake air temperature sensor. Examples include ignition timing control, boost pressure control for a turbo-charger, limiter control for fuel injection volume in rapid acceleration, and judgment as to whether the catalyst used has reached an active catalyst temperature.
It is an object of the present invention to provide an air flow sensor capable of being rendered integral with an intake air temperature sensor, thereby capable of attaining the reduction in the number of sensor components, reduction of cost and rationalization of the mounting work and mounting space, and further capable of keeping high the accuracy of the intake air temperature sensor.
It is another object of the present invention to provide a thermal air flow sensor which, even when an intake air temperature sensing element (the type of use does not matter specially) and a thermal air flow measuring element are mounted on a common support member in case of uniting the intake air temperature sensing element with the air flow sensor, can fully eliminate a thermal influence from a heating resistor and circuit section of the air flow measuring element and from an engine. Therefore it is to provide a thermal air flow sensor which can enhance the intake air temperature measurement accuracy and which can maintain the soundness of the intake air temperature sensing element even when placed in a metal corrosion inducing environment containing moisture present in the intake air, gasoline vapor, engine oil, and sulfurous acid gas and nitrogen oxides present in blow-by gas.
According to the present invention, for achieving the above-mentioned objects, there basically is provided a thermal air flow sensor having a thermal element for measuring the air flow flowing through an intake passage, the thermal air flow measuring element having a heating resistor and being disposed within the intake passage, wherein an intake air temperature sensing element used in an intake air temperature sensor is mounted on a single support member made of a glass-ceramic material etc together with the air flow measuring element and is positioned within the intake passage. Moreover, the air flow measuring element and the intake air temperature sensing element are electrically connected respectively to conductors disposed on the support member and the resulting electric connections are sealed with resin.
According to the present invention, moreover, there is adopted a structure wherein both sides of a portion of the support member located on the side apart from the wall of an intake pipe are easy to be taken away their heat by an air flow moving through the intake pipe. On such a heat-removed substrate side there are provided the air flow measuring element and the intake air temperature sensing element.
The present invention further proposes the following thermal air flow sensors.
One is a thermal air flow sensor having an intake air temperature sensing element, wherein this intake air temperature sensing element and the foregoing air flow measuring element are mounted on a single glass-ceramic or ceramic support member and are positioned within the intake passage, the support member is cantilevered by means of a holder attached to the wall of the intake pipe, and the intake air temperature sensing element is disposed at one end of the support member on the side opposite to the cantilevered side and at a position away from the holder with respect to the air flow measuring element. The air flow measuring element and the intake air temperature sensing element are electrically connected respectively to conductors disposed on the support member and the resulting electric connections are sealed with resin.
Another is a thermal air flow sensor having a structure whereby both sides of a portion of the support member located on the side away from the wall of the intake pipe are easy to be taken away their heat by an air flow moving through the intake pipe. On such a heat-removed support member side there are disposed the air flow measuring element and the intake air temperature sensing element.
A still another is a thermal air flow sensor wherein the air flow measuring element and the intake air temperature sensing element are respectively mounted in recesses formed each individually in the support member and are electrically connected respectively to conductors disposed on the support member. The resulting electric connections are sealed with resin.